check for duplicated stack addresses by JimLee168

Based on https://code.google.com/p/jpcsp/source/detail?r=3569

Fix WWE SmackDown! vs. RAW 2006,2007,2008 booting
Fix #6671

2006 Modify log: https://gist.github.com/sum2012/a74a7199dcb3058fa5d8
Also, there's no need for this to be a `u32_le`, since it doesn't live in memory.  Making it a `u32` might slightly unnoticeably improve performance on big endian (which we don't have any active ports of...)

Doesn't really matter.

-[Unknown]